Why doesn't this code do what I'd expect it to, and how can I fix it?

    unittest{
        import std.traits : Parameters;
        // Works as expected
        alias dg = int delegate(int value);
        enum bool dgcallable = is(typeof((){dg(Parameters!dg.init);}));
        pragma(msg, dgcallable); // Prints true
        // Doesn't work as expected
        alias dgref = int delegate(ref int value);
        enum bool dgrefcallable = is(typeof((){dgref(Parameters!dgref.init);}));
        pragma(msg, dgrefcallable); // Prints false
    }

Thanks!

On Thursday, 28 July 2016 at 19:19:06 UTC, pineapple wrote:
> Why doesn't this code do what I'd expect it to, and how can I fix it?
>
>     unittest{
>         import std.traits : Parameters;
>         // Works as expected
>         alias dg = int delegate(int value);
>         enum bool dgcallable = is(typeof((){dg(Parameters!dg.init);}));
>         pragma(msg, dgcallable); // Prints true
>         // Doesn't work as expected
>         alias dgref = int delegate(ref int value);
>         enum bool dgrefcallable = is(typeof((){dgref(Parameters!dgref.init);}));
>         pragma(msg, dgrefcallable); // Prints false
>     }
>
> Thanks!

"Parameters!dgref.init" does not yield a reference. The real error is not displayed. In a normal context it would be "stuff is not callable with...."

On Thursday, 28 July 2016 at 20:28:39 UTC, jdfgjdf wrote:
> "Parameters!dgref.init" does not yield a reference. The real error is not displayed. In a normal context it would be "stuff is not callable with...."

What would be a better way to check whether some callable can be called using a parameters tuple?

On Thursday, 28 July 2016 at 21:49:00 UTC, pineapple wrote:
> On Thursday, 28 July 2016 at 20:28:39 UTC, jdfgjdf wrote:
>> "Parameters!dgref.init" does not yield a reference. The real error is not displayed. In a normal context it would be "stuff is not callable with...."
>
> What would be a better way to check whether some callable can be called using a parameters tuple?

http://dlang.org/phobos/std_traits#.lvalueOf

On Thursday, 28 July 2016 at 21:49:00 UTC, pineapple wrote:
> On Thursday, 28 July 2016 at 20:28:39 UTC, jdfgjdf wrote:
>> "Parameters!dgref.init" does not yield a reference. The real error is not displayed. In a normal context it would be "stuff is not callable with...."
>
> What would be a better way to check whether some callable can be called using a parameters tuple?

Oh, I answered my own question

    enum bool dgrefcallable = is(typeof((){auto params = Parameters!dgref.init; dgref(params);}));